Mems device fabricated on a pre-patterned substrate

ABSTRACT

A microelectromechanical systems device fabricated on a pre-patterned substrate having grooves formed therein. A lower electrode is deposited over the substrate and separated by an orthogonal upper electrode by a cavity. The upper electrode is configured to be movable to modulate light.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/174,220, filed Jul. 1, 2005, which claims priority to U.S.Provisional Application No. 60/613,376, filed Sep. 27, 2004. Thedisclosures of the foregoing applications are hereby incorporated byreference in their entireties.

BACKGROUND

1. Field

The field of the invention relates to microelectromechanical systems(MEMS) and the packaging of such systems. More specifically, the fieldof the invention relates to interferometric modulators and methods offabricating such interferometric modulators on a pre-patternedsubstrate.

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap or cavity. As described herein in more detail, the position ofone plate in relation to another can change the optical interference oflight incident on the interferometric modulator. Such devices have awide range of applications, and it would be beneficial in the art toutilize and/or modify the characteristics of these types of devices sothat their features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF CERTAIN EMBODIMENTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices. The embodiments described herein provide a package structureand a method of manufacturing a package structure in ambient conditions.

An embodiment provides a method of making a microelectromechanicalsystems device. A substrate having a plurality of trenches is provided.At least one layer is deposited over the substrate, wherein the layer isdiscontinuous at the trenches. A first cavity is created between a firstelectrode formed over the substrate and a second electrode, wherein theat least one layer comprises the first electrode.

According to another embodiment, a display device is provided,comprising a substrate having a plurality of grooves formed therein, afirst electrode formed over a top surface of the substrate and a secondelectrode, a semi-reflective layer, and a transparent material formedover the chromium layer. The first electrode and the second electrodeare insulated from each other and separated by a first cavity. Thesemi-reflective layer separated from the second electrode by a secondcavity.

According to yet another embodiment, a method of forming amicroelectromechanical systems device is provided. A substrate having atop surface is provided, wherein a plurality of grooves is formed in thetop surface. At least one layer is deposited over the substrate, whereinthe at least one layer comprises a first conductive material and isdiscontinuous at the grooves forming rows of the layer on the topsurface. A second conductive material is deposited, wherein the secondconductive material is oriented orthogonally to the first conductivematerial on the top surface.

In accordance with another embodiment, a display device is provided. Thedisplay device comprises a substrate having a plurality of groovesformed therein, a first reflecting means for reflecting light formedover a top surface of the substrate and a second reflecting means forreflecting light, a semi-reflective layer separated from the secondreflecting means by a second cavity, and a viewing means fortransmitting light. The first reflecting means and the second reflectingmeans are insulated from each other and separated by a first cavity, andthe viewing means formed over the semi-reflective layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be readily apparent fromthe following description and from the appended drawings (not to scale),which are meant to illustrate and not to limit the invention, andwherein:

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIGS. 8A-8C are cross-sections of an interferometric modulator formed on a pre-patterned substrate, in accordance with an embodiment.

FIG. 8D is a cross-section of an interferometric modulator formed on apre-patterned substrate, in accordance with another embodiment.

FIG. 8E is a cross-section of an interferometric modulator formed on apre-patterned substrate, in accordance with yet another embodiment.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. In some embodiments, the layers are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias). As is also illustrated in FIG.4, it will be appreciated that voltages of opposite polarity than thosedescribed above can be used, e.g., actuating a pixel can involve settingthe appropriate column to +V_(bias), and the appropriate row to −ΔV. Inthis embodiment, releasing the pixel is accomplished by setting theappropriate column to −V_(bias), and the appropriate row to the same−ΔV, producing a zero volt potential difference across the pixel. As isalso illustrated in FIG. 4, it will be appreciated that voltages ofopposite polarity than those described above can be used, e.g.,actuating a pixel can involve setting the appropriate column to+V_(bias), and the appropriate row to −ΔV. In this embodiment, releasingthe pixel is accomplished by setting the appropriate column to−V_(bias), and the appropriate row to the same −ΔV, producing a zerovolt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 44, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor -21is also connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28, and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one oremore devices over a network. In one embodiment the network interface 27may also have some processing capabilities to relieve requirements ofthe processor 21. The antenna 43 is any antenna known to those of skillin the art for transmitting and receiving signals. In one embodiment,the antenna transmits and receives RF signals according to the IEEE802.11 standard, including IEEE 802.11(a), (b), or (g). In anotherembodiment, the antenna transmits and receives RF signals according tothe BLUETOOTH standard. In the case of a cellular telephone, the antennais designed to receive CDMA, GSM, AMPS or other known signals that areused to communicate within a wireless cell phone network. Thetransceiver 47 pre-processes the signals received from the antenna 43 sothat they may be received by and further manipulated by the processor21. The transceiver 47 also processes signals received from theprocessor 21 so that they may be transmitted from the exemplary displaydevice 40 via the antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecomers only, on tethers 32. In FIG. 7C, the moveable reflective layer 14is suspended from a deformable layer 34, which may comprise a flexiblemetal. The deformable layer 34 connects, directly or indirectly, to thesubstrate 20 around the perimeter of the deformable layer 34. Theseconnections are herein referred to as support posts. The embodimentillustrated in FIG. 7D has support post plugs 42 upon which thedeformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support postsare formed of a planarization material, which is used to form supportpost plugs 42. The embodiment illustrated in FIG. 7E is based on theembodiment shown in FIG. 7D, but may also be adapted to work with any ofthe embodiments illustrated in FIGS. 7A-7C as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. Such shielding allows the bus structure 44in FIG. 7E, which provides the ability to separate the opticalproperties of the modulator from the electromechanical properties of themodulator, such as addressing and the movements that result from thataddressing. This separable modulator architecture allows the structuraldesign and materials used for the electromechanical aspects and theoptical aspects of the modulator to be selected and to functionindependently of each other. Moreover, the embodiments shown in FIGS.7C-7E have additional benefits deriving from the decoupling of theoptical properties of the reflective layer 14 from its mechanicalproperties, which are carried out by the deformable layer 34. Thisallows the structural design and materials used for the reflective layer14 to be optimized with respect to the optical properties, and thestructural design and materials used for the deformable layer 34 to beoptimized with respect to desired mechanical properties.

As discussed above, the interferometric modulator is configured toreflect light through the transparent substrate and includes movingparts, such as the movable mirrors 14 a, 14 b. Therefore, to allow suchmoving parts to move, a gap or cavity is preferably created to allow themechanical parts, such as the movable mirrors 14 a, 14 b, of theinterferometric modulator to move.

FIGS. 8A-8C are cross-sectional views of an interferometric modulatorformed on a pre-patterned substrate, in accordance with an embodiment.It has been found that the steps involved in producing interferometricmodulators that function as described above are adaptable to very costeffective production techniques when a pre-patterned substrate is used.FIGS. 8A-8C illustrate one embodiment of such a method, which results inan interferometric modulator that is viewed from the opposite side asthe interferometric modulator described above with reference to FIGS.1-7E. Depending on the final application of the device, it willsometimes be preferable to produce a display viewed through thesubstrate, and sometimes preferable to produce a display viewed throughthe deposited layers of the interferometric modulator. Thus, with such adesign, it is not necessary to use a transparent substrate (such astransparent substrate 20, shown in FIGS. 7A-7E) on which to form theinterferometric modulator. The pre-patterned substrate may therefore beeither opaque or transparent. In the illustrated embodiment shown inFIGS. 8A-8C, the pre-patterned substrate is preferably non-transparent,which allows for a selection of materials that are conducive toembossing.

According to the embodiment shown in FIGS. 8A-8C, an interferometricmodulator is formed on a pre-patterned substrate 505. A substrate 505having trenches 507 formed therein is preferably covered with a mirrorlayer to form a lower electrode (a semi-reflecting or reflecting means)502, which will serve as the fixed layer described above.

The substrate 505 may be formed from a preferably non-transparentpolymer material having a series of embossed, appropriately spacedgrooves or trenches 507 running in one direction along the substratesurface. These grooves 507 may be embossed using known techniques in avariety of conventional materials to preferably have a reentrant profilewith tapering sides, as shown in FIGS. 8A-8C. In a preferred embodiment,a substrate 505 formed of a composite material is embossed, stamped,ablated, molded, or mechanically imprinted with trenches or grooves, andsubsequently baked to obtain the reentrant profile. The skilled artisanwill appreciate that such a composite material is preferably formed ofdifferent materials in different layers and that after stamping orembossing the substrate, baking causes differential thermal expansion inthe different layers. In the illustrated embodiment, the top layer(s)have a higher coefficient of thermal expansion, thereby causingexpansion into the grooves 507. Although the reentrant profile ispreferred, the skilled artisan will appreciate that the grooves 507 mayhave other shapes (e.g., vertical walls) so long as the grooves cause abreak in material deposited over the top surface of the substrate 505,as discussed in more detail below. It will be understood that thegrooves 507 may be formed in the substrate 505 by techniques other thanembossing, such as, for example, etching. However, embossing or stampingis preferred as it is an inexpensive process.

When material is deposited on such a surface structure, some materialwill be deposited and settle into the grooves 507, and some materialwill be deposited and settle on the top surface of the substrate 505between the grooves 507. The material is preferably deposited byconventional deposition techniques, such as some form of sputtering,physical vapor deposition, and chemical vapor deposition (CVD). As shownin FIGS. 8A-8C, the presence of the grooves 507 produces breaks ordiscontinuities in the deposited layers on the top surface of thesubstrate 505. In this way, the lower layers 502, 508, 510 of theinterferometric modulator structure are deposited without theconventional photolithography and etching steps. In this embodiment,effectively, the first set of masks that produces the structure of FIGS.7A-7E is incorporated into the substrate 505 itself, and conventionalmasking can, in fact, be replaced by economical embossing processes forthe initial electrode pattern. According to this embodiment, the firststeps of interferometric modulator structure fabrication are thusdepositing the lower electrode 502, a dielectric material 508, and alayer of sacrificial material 510. The layers of the deposited lowerelectrode 502, dielectric material 508, and sacrificial material 510 arethus formed in rows or strips on the top surface of the substrate 505.The strip structure is produced naturally by the presence of theembossed grooves 507.

The lower electrode 502 is preferably formed of aluminum. In otherembodiments, the lower electrode 502 may comprise other highlyreflective metals, such as, for example, silver (Ag) or gold (Au).Alternatively, the lower electrode 502 may be a stack of metalsconfigured to give the proper optical and mechanical properties.

A dielectric layer 508 is preferably deposited over the lower electrode502. In a preferred embodiment, the dielectric material is silicondioxide (SiO₂). A sacrificial layer 510 is preferably deposited (andlater removed) over the structure to create a resonant optical cavitybetween the lower electrode 502 and an upper electrode or reflectingmeans 506 that will be deposited over the sacrificial layer 510 to formthe movable layer, as shown in FIG. 8B. In the illustrated embodiment,the sacrificial layer 510 comprises silicon (Si). In other embodiments,this sacrificial layer 510 may be formed of molybdenum (Mo), tungsten(W), or titanium (Ti). All of these sacrificial materials can beselectively etched, relative to the exposed dielectric and electrodematerials, but the skilled artisan will readily appreciate that othersacrificial materials (e.g., photoresist) can be used with otherselective etch chemistries.

As shown in FIG. 8B, in this embodiment, interferometric modulatorstructure production is continued by filling the trenches 507 and theregions between the previously deposited structures. This filling can bedone with many conventional deposition/pattern/etch steps or with anetch back process, such as chemical mechanical polishing (CMP)planarization step, for example.

Orthogonal upper electrode strips 506 are preferably deposited over thesacrificial layer 510, followed by strips of a second or uppersacrificial material 520 separated by posts 522. This upper electrode506 is deposited as strips in rows orthogonal to the lower electrode 502rows to create the row/column array described above. The upper electrode506 and sacrificial material 520 may be deposited as strips in theirdesired patterns, preferably using a shadow mask deposition technique.The posts 522 are formed of insulating materials, preferably a polymeror dielectric material.

A thin, preferably 50-100 angstrom, semi-reflective layer 530 is thenpreferably deposited over the upper sacrificial layer 520. In apreferred embodiment, the semi-reflective layer 530 is chromium. Asshown in FIG. 8B, a transparent material or viewing means 535 isdeposited over the semi-reflective layer 530 to provide additionalmechanical and structural integrity to the semi-reflective layer 530,which is typically too thin to support itself after removal of thesacrificial layers 510, 520. The skilled artisan will understand thatthe transparent substrate 535 serves a mechanical function as well as ameans through which display takes place and through which light istransmitted. The transparent substrate 535 may be formed of a solidinorganic material, such as an oxide. In another embodiment, thetransparent substrate 535 may be formed of a transparent polymer. Thesemi-reflective layer 530 and the transparent substrate are preferablydeposited by conventional deposition techniques, such as sputtering,PVD, and CVD.

The transparent material 535 and semi-reflective layer 530 arepreferably etched with openings or holes (not shown) so that the etchgas used for sacrificial layer removal can reach the sacrificialmaterial of layers 510 and 520. Alternatively, the transparent material535 may be pre-patterned with openings or holes that are pre-etched orembossed. It will be understood that, as part of the overall packagingprocess, the interferometric modulators are sealed and protected fromthe environment surrounding the package containing the interferometricmodulators. Preferably, the holes or openings have a diameter as smallas the photolithographic system will permit, and more preferably about2.4 microns. The skilled artisan will understand that the size, spacing,and number of openings will affect the rate of removal of thesacrificial layers 510, 520.

The sacrificial layers 510, 520 are removed, preferably using aselective gas etching process, to create the optical cavity around themovable electrode 506. Standard etching techniques may be used to removethe sacrificial layers 510, 520. The particular gas etching process willdepend on the material to be removed. For example, xenon diflouride(XeF₂) may be used as the release gas for removing a silicon sacrificiallayer. It will be understood that the etching process is a selectiveetching process that does not etch any dielectric, semi-reflecting, orelectrode materials.

The final structure of the interferometric modulator is shown in FIG.8C, where there is an optical cavity surrounding the moving electrode506. Because the semi-reflective layer 530 is on top, theinterferometric modulator is viewed through the transparent substrate535 from the side of the deposited layers in the direction of arrow 540,as shown in FIG. 8C.

In the embodiment shown in FIG. 8A-8C, it will be understood that themovable layer 506 of the interferometric modulator is adjacent thetransparent substrate 535 and the fixed layer 502 is formed below themovable layer 506 such that the movable layer 506 may move within theoptical cavity of the structure, as shown in FIG. 8C.

The skilled artisan will appreciate that, in the embodiment shown inFIG. 8D, the semi-reflective layer 530 is preferably chromium and can besupplemented with a transparent electrode, preferably an ITO layer, andused as an electrode. As shown in FIG. 8D, the ITO layer 532 is betweenthe transparent substrate 535 and the chromium layer 530. ThisITO-chromium bilayer structure eliminates the need for the lowerelectrode 502 and dielectric 508 of the embodiment shown in FIGS. 8A-8C.In this embodiment, a dielectric layer 508 is between the chromium 530and the upper cavity. The skilled artisan will appreciate that a firstsacrificial layer (not shown) is deposited on the pre-patternedtransparent substrate 505 and later removed to form a lower cavity 560,and a second sacrificial layer (not shown) is deposited over theelectrode 506 to form the upper cavity 565. As shown in FIG. 8D, theelectrode 506 is deposited over the pre-patterned substrate 505 formingelectrode strips on the top surface of the substrate 505, where thediscontinuities in the electrode 506 are caused by deposition over thetrenches 507.

As mentioned above, transparent pre-patterned substrates made fromtransparent materials, such as polymers, may be used to create aninterferometric modulator similar to that shown in FIGS. 7A-7E. In suchan interferometric modulator, as shown in FIG. 8E, unlike the embodimentshown in FIGS. 8A-8C, the transparent pre-patterned substrate 580transmits light and viewing takes place through the transparentpre-patterned substrate 580. The skilled artisan will understand thatthe process for making such an interferometric modulator is similar tothe method described above with reference to FIGS. 8A-8C, but that theelectrode structure would be reversed. The structure would be similar tothat of FIGS. 7A-7E, but the first few patterning and etching steps tocreate the rows are eliminated by depositing the first layers in rowsover the trenches 507.

As shown in FIG. 8E, the semi-reflective-ITO bilayer 530, 532 isdeposited over the substrate 580 to form electrode strips. A dielectriclayer 508 is deposited over the semi-reflective-ITO bilayer 530, 532. Afirst sacrificial layer (not shown) is then deposited and later removedto form a lower cavity 560. The movable electrode 506 is deposited inorthogonal strips over the first sacrificial layer. A second sacrificiallayer (not shown) is deposited over the movable electrode 506 and laterremoved to form the upper cavity 565. As shown in FIG. 8E, the movableelectrode 506 is in a collapsed state. To complete the structure, adeformable layer 570 is formed over the upper cavity 565.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A microelectromechanical systems (MEMS) device, comprising: asubstrate including a top surface and a plurality of trenches formed inthe top surface, the trenches being spaced from one another; a firstelectrode layer formed over the top surface of the substrate, whereinthe first electrode layer is discontinuous at the trenches to therebyseparate the first electrode layer into a plurality of portions; and asecond electrode formed over the first electrode, the second electrodebeing separated from the first electrode by a cavity.
 2. The device ofclaim 1, wherein the trenches extend substantially parallel to oneanother.
 3. The device of claim 2, wherein the plurality of portionscomprise rows of first electrodes.
 4. The device of claim 3, wherein thesecond electrode forms an elongated strip, and wherein the rows of firstelectrodes are orthogonal to the second electrode.
 5. The device ofclaim 1, wherein the first electrode layer comprises a first material,and wherein the device further comprises the first material on bottomsurfaces of the trenches.
 6. The device of claim 1, wherein thesubstrate is formed of a substantially transparent material.
 7. Thedevice of claim 6, wherein the first electrode layer comprises atransparent electrode layer.
 8. The device of claim 7, furthercomprising an absorber layer adjacent the transparent electrode layer.9. The device of claim 8, further comprising a dielectric layer over theabsorber layer and the transparent electrode layer.
 10. The device ofclaim 1, wherein the second electrode comprises an at least partiallyreflective layer facing the cavity.
 11. The device of claim 1, whereinat least one of the trenches includes a reentrant profile.
 12. Thedevice of claim 1, wherein the second electrode is configured to bemovable toward the first electrode layer.
 13. The device of claim 1,wherein the cavity is smaller when the second electrode is moved towardthe first electrode layer.
 14. The device of claim 1, wherein the MEMSdevice comprises an interferometric modulator.
 15. Amicroelectromechanical systems (MEMS) device, comprising a substratehaving a top surface and a plurality of grooves formed in the topsurface; a plurality of first electrode strips formed over the topsurface of the substrate and electrically separated from one another bythe grooves; and a second electrode formed over the first electrodestrips and separated from the first electrode strips by cavities. 16.The device of claim 15, wherein the plurality of grooves include bottomsurfaces, and wherein the top surface of the substrate and the bottomsurfaces of the grooves are formed of the same material as each other.17. The device of claim 15, wherein the substrate is formed of acomposite material.
 18. The device of claim 17, wherein the substratecomprises multiple layers formed of materials different from oneanother.
 19. The device of claim 15, wherein the first electrode stripscomprise a conductive material, and wherein the device further comprisesthe conductive material in the grooves, the conductive material in thegrooves being electrically separated from the first electrode strips.20. The device of claim 15, further comprising a plurality of dielectricstrips, each of the dielectric strips being formed of a dielectricmaterial over a respective one of the first electrode strips, whereinthe device further comprises the dielectric material in the grooves, thedielectric material in the grooves being discontinuous from thedielectric strips.
 21. The device of claim 15, wherein the cavitiescomprise a plurality of air gaps defined between the first electrodestrips and the second electrode.
 22. The device of claim 15, wherein thesubstrate is formed of a substantially transparent material, whereineach of the first electrode strips comprises a partially transparentlayer, and wherein the second electrode comprises an at least partiallyreflective layer.
 23. The device of claim 15, wherein the substrate isformed of an opaque material, wherein each of the first electrode stripscomprises an at least partially reflective layer, and wherein the secondelectrode comprises a partially transparent layer.
 24. The device ofclaim 15, wherein the second electrode is configured to be movabletoward the first electrode strips.
 25. The device of claim 15, furthercomprising a semi-reflective layer formed over the second electrode andseparated from the second electrode by a second cavity.
 26. The deviceof claim 25, further comprising a transparent layer formed over thesemi-reflective layer.
 27. The device of claim 15, wherein the MEMSdevice comprises an interferometric modulator.